1. Field of the Invention
This invention relates to an image reading apparatus such as a facsimile apparatus arranged to be capable of processing image data for communicating or copying the image data.
2. Description of Related Art
Image reading apparatuses, such as facsimile apparatuses, arranged to read image data and to send the image data to a communication line or some other apparatus or to copy the image data are popularly in use.
The image reading apparatus of such a kind is provided with a driving part for feeding an original. A stepping motor (also known as pulse motor) is most popularly employed as a driving motor for use in the driving part, because the stepping motor is easily controllable and gives a high degree of feeding precision.
As for an image reading sensor of the image reading apparatus, a line sensor or the like is employed. Main scanning which is to be made in the horizontal direction of the original is performed by the line sensor, while sub-scanning which is to be made in the vertical direction of the original is performed by feeding the original by the driving part. Thus, the resolution of the image in the main scanning direction is determined according to the number of picture elements of the line sensor, and the resolution of the image in the sub-scanning direction is determined according to the driving pitch of the driving motor of the driving part.
In the meantime, a mm (millimeter) unit system is generally used for defining the image resolution in the direction of sub-scanning, i.e., as a unit system for feeding the original. The driving steps of the pulse motor used for image reading fundamentally corresponds to the density of sub-scanning, and the pulse motor is driven by driving steps in the mm unit system.
FIG. 1 is a block diagram showing in outline the arrangement of a driving system used for sub-scanning in the above-stated image reading apparatus.
Referring to FIG. 1, a pulse motor driving device 1 for feeding the original is composed of a hardware logic circuit which includes a number of counters, registers, etc. A main control part 2 is composed of a microprocessor and is arranged to control actions of the whole apparatus including the pulse motor driving device 1. A pulse motor driving circuit 3 is arranged to drive a pulse motor 4 in accordance with driving data supplied from the pulse motor driving device 1, by applying an exciting output for each phase of the pulse motor 4.
Image scanning means 5 is arranged to read image data on a paper surface being transported by the driving action of the pulse motor 4. The image scanning means 5 includes a scanner part 6 which is provided with a line sensor, etc., for horizontally scanning the image of the original, and a paper sensor 7 which is arranged to detect the original being transported by the pulse motor 4. These parts are respectively arranged to operate under the control of the main control part 2.
A RAM (random access memory) 8 stores data which can be set as desired by the operator of the apparatus. A ROM (read only memory) 9 stores beforehand a program, a message of the operator, etc., for controlling the main control part 2 which is composed of a microprocessor, etc. Reference numeral 10 denotes the entirety of an image communication apparatus, such as a facsimile apparatus, configured as described above.
FIG. 2 schematically shows in a block diagram the internal arrangement of the pulse motor driving device 1. Referring to FIG. 2, a synchronizing circuit 11 is arranged to synchronize with each other an image scan timing signal for scanning an image by the line sensor and a driving trigger signal for the pulse motor 4 for feeding the original. The synchronizing circuit 11 operates under the control of a clock signal (clk) supplied from a clock signal oscillator (not shown). A motor counter 12 is arranged to count the pulses of a motor driving pulse signal outputted from the synchronizing circuit 11 for actually driving the pulse motor 4. An exciting pattern selector part 13 is arranged to select and output driving waveform data for actually driving the pulse motor 4 on the basis of the output of the motor counter 12. An exciting pattern storing part 14 is arranged to store the exciting pattern for driving the pulse motor 4.
FIG. 3 is a timing chart showing the actual actions of the device shown in FIG. 2 in the above-stated mm unit system. Referring to FIG. 3, the image scan timing signal for image reading is inputted in a predetermined cycle. The driving trigger signal for feeding the original is inputted at random. An actual motor driving signal, i.e., a timing signal for feeding the original, is formed by synchronizing with each other the image scan timing signal and the driving trigger signal. An image reading action in the mm unit system is performed while feeding the original at a pitch in the mm unit system according to the actual motor driving signal.
The image reading can be accurately carried out in the mm unit system. However, at present, a unit called "DPI" (dot per inch) is most popularly used as the unit of image resolution for business machines such as copying machines, peripheral apparatuses for computers, etc., that is, an inch unit system is generally used for the image resolution. Therefore, in a case where an image read out by a facsimile apparatus or the like is to be recorded by a peripheral apparatus operating in the inch unit system, it has been practiced in general to carry out a mm/inch conversion process (conversion from the mm unit system to the inch unit system) either by a software process or a hardware process before recording, because pitches in the sub-scanning direction of these apparatuses would not match with each other without the mm/inch conversion process.
However, according to the conventional method mentioned above, the resolution obtained at the time of image reading is in the mm unit system and the data matching to the inch unit system is formed by the image processing action. The recording is thus performed not by exactly reading the image with its resolution in the inch unit system. Therefore, it has been desired to have an apparatus which is capable of carrying out the above-stated conversion in cases where an image must be obtained with its resolution in the inch unit system at the time of reading, that is, in cases where the image is to be copied or the image data is to be supplied to a peripheral apparatus or where the image data is to be outputted without recourse to a telephone line.